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The historically unstable Sunkist Bay cliff in Auckland, New Zealand, is formed of weak Pleistocene alluvial sediments, infilling a paleovalley eroded into Miocene sandstone. Weathered tephra layers dip at low angles out of the cliff, and part-control stability. The last major failure prior to 2017 occurred in 2011, immediately to the west of the 2017 failure. Despite the long-term history of instability, over the last two decades, residential property construction has continued to

The 2208 km2 Waipaoa River catchment, the onshore portion of the Waipaoa source-to-sink (S2S) sedimentary system in the East Coast of New Zealand’s North Island, is a tremendously data-rich study area for obtaining insights into catchment function and connectivity (Kuehl et al. 2016). There have been longstanding concerns about erosion severity and mitigation dating back to 1895 (Hill, 1895). High rates of erosion in the Waipaoa have been the defining catchment management issue since the mid-twentieth century, triggered by forest clearance for pastoral agriculture in the late nineteenth and early twentieth century and primed by a combination of highly erodible lithologies, steepland terrain, regular intense storm events, and slopes undercut by postglacial river incision. The magnitude of erosion in the East Coast Region since European forest clearance has exceeded that in any other part of New Zealand. Connectivity relationships in the Waipaoa catchment have been profoundly altered. Simultaneous sediment inputs from deforested slopes deliver sediment directly into tributary and trunk stream channels, causing significant bed aggradation and channel infilling. Gullies overwhelm receiving streams, forming alluvial fans and represent the single largest source of sediment to the system. Sediment derived from shallow landslides is significant during storm events, but gully, sheet and riverbank erosion have the potential to generate sediment whenever it rains. In the upper catchment, channel widening contributes further sediment, particularly through bank and cliff erosion. The fine-grained nature of sediment supplied by lithologies in the upper catchment accentuates downstream delivery of materials, resulting in channel contraction and floodplain accretion in the lower Waipaoa. Efforts to mitigate erosion by afforestation using plantation forestry have been successful in some headwater tributaries, with channel degradation beginning, but this process generates additional sediment, which is conveyed downstream. We use a combination of LiDAR and river channel cross-sections to demonstrate contemporary longitudinal patterns of connectivity in the Waipaoa River and assess the prospective river futures of this anthropogenically altered system. ReferencesHill, H. (1895) Denudation as a factor of Geological Time. Transactions and Proceedings of the New Zealand Institute, 1895, Volume XXVIII.Kuehl, S. A., Alexander, C. R., Blair, N. E., Harris, C. K., Marsaglia, K. M., Ogston, A. S., Orpin, A. R., Roering, J. J., Bever, A. J. & Bilderback, E. L. 2016. A source-to-sink perspective of the Waipaoa River margin. Earth-Science Reviews, 153, 301-334.

Globally, fluvial systems are under considerable and increasing threat from a plethora of anthropogenic stresses. These include different types of indirect (e.g. land cover/use or climate change) and direct human impacts (e.g. river engineering) that alter water and sediment dynamics. It is widely known that (dis)connectivity relationships in river and catchment systems determine the source, timing and rates of water and sediment flux and thus their geomorphic sensitivity and response to disturbance. However, most river and catchment management plans overlook the role of sediment (dis)connectivity. Here we use examples from different environmental settings with different sediment-related problems to show how understandings of sediment (dis)connectivity can inform catchment-based management. Specifically, we focus on concerns for river conservation and recovery, using examples from Austria, New Zealand and Australia. Moreover, we present questions for practitioners to appropriately contextualise (dis)connectivity concepts in system-specific place-based management applications.

Seismic shaking in mountain environments introduces the potential for complex fluvial response from a multitude of landslide sources. Stream networks may be impacted in multiple branches, introducing the possibility of interacting sedimentary ‘pulses’ moving through the system. Large quantities of mobile sediment added to the stream network from multiple sources during and after a co-seismic event can overload susceptible river reaches, causing changes in sediment transport and storage. Although past research works have addressed dynamic sediment movement in river networks and identification of sedimentary hotspots, the physiographic factors (e.g. canyons, bends, fans, slope change) that prompt such change remain unexplored. The catchment settings and reach sequences that contribute most to delay/acceleration of the sediment in the active mountain environments are investigated in order to improve hazard assessment in susceptible terrain. In this work, we employ the one-dimensional River Network Bed-Material Sediment model (Czuba & Foufoula-Georgiou, 2014) to explore the landscape factors that may lead to hotspot behaviour for the very coarse sand fraction (2mm), followed by multi-criteria analysis of four basic stream network parameters: slope, sinuosity, channel confinement and tributary influence. Patterns of network topology associated with delay and accumulation of river sediment in the model were systematically identified in 75,400 stream links from 16 major drainages (135 to 6425 km2) of New Zealand’s upper South Island, as assessed by sediment travel time and the cluster persistence index (CPI). Catchment size determines the number of sediment sources, and thus ultimately the magnitude of the sedimentary hotspots i.e., bigger catchments can accommodate more landslides which increases the sediment input, along with the chances of sediment accumulation at susceptible locations. Multi-criteria analysis of the top 10 reaches with highest CPI values in each catchment (160 sites, total), showed that about 30% of the hotspots occurred in partly-confined valley settings with gentle slope (

Recently uplifted, soft Pleistocene sediments in northern New Zealand are particularly vulnerable to landsliding because they are often underlain by less permeable, clay-rich Neogene mudstone–siltstone rocks. Typically, instability is rainfall-induced, often owing to a high-intensity rainfall event from extra-tropical cyclones, following wetter months when antecedent soil moisture has increased. Using remote sensing, field surveys and laboratory testing, we report on some emerging slope instability hazards in the eastern suburbs of the coastal city of Gisborne, on the North Island. Retrogressive failure of the main landslide (at Wallis Road) is continuing and has already led to the abandonment of one dwelling, and an adjacent landslide (at Titirangi Drive) appears to be in an incipient phase of failure. The Wallis Road landslide has been particularly active from mid-2017, with slumping of the headscarp area changing to a constrained mudflow downslope, which then descends a cliff before terminating on the beach. In contrast, the incipient Titirangi Drive landslide at present displays much more subtle effects of deformation. Although activity at both landslides appears to be linked to rainfall-induced increases in soil moisture, this is due to the effects of prolonged periods of rainfall rather than the passage of high-intensity cyclonic storms.

Large Wood (LW) transported during floods or channelized mass flows poses a high risk for engineered structures, often leading to significant damage or total failure of the impacted structure. To date little is known about impact magnitudes caused by LW collisions. To better control for such interactions, a better understanding of transport dynamics and impact forces is required. The present laboratory study employs state-of-the-art sensor units installed in scaled logs to capture acceleration data from collisions of waterborne LW with 2 in-stream structures-bridge pier and retention structure-each providing different examples of rigid engineered systems. Through precise measurements of acceleration and impact duration (stopping time), the resultant impact forces of LW collisions can be calculated. Here, for the first time, impact forces were quantified in a scaled stream environment based on the inertial frame of the object causing the impact, rather than the more commonly used instrumented structure approach. High-resolution accelerometer measurements were compared to conventional analytical (force balance) approaches. They revealed the need for accurate inertia measurements to appropriately account for prevailing hydraulic flow conditions and the effects of LW interactions in fluvial environments. Although log velocity and stopping time are crucial parameters for assessing LW impact forces, accurate measurements are still elusive due to limitations in available sensing techniques. By presenting proof-of-concept results, this study contributes to an improved understanding of LW impact forces during floods. Based on these encouraging results, we recommend more sensor-based field studies in future, needed for the design of resilient structures., Natural Hazards, 113 (3), ISSN:0921-030X, ISSN:1573-0840

Landslides are widespread natural hazards that are responsible for substantial economic and societal damage globally each year. In New Zealand, landslides frequently occur on soil and rock, triggered by high rainfall, seismic activity, and land-use change and/or disturbance. This study focuses on Gisborne, a city where ongoing slope instability issues occurring across the steep slopes within the urban area are affecting several properties. Failure commonly occurs along reactivated slip surfaces, when slow-moving retrogressive slides transition into fast-moving flows during intense rainfall events. However, the extent and rate of slope deformation in the Gisborne area are poorly known. Spaceborne Interferometric synthetic aperture radar (InSAR) is a convenient method for measuring ground deformation and over the past decade, SAR systems have significantly developed and provide consistent, reliable, high-resolution global data. In particular, the launch of Sentinel-1 in 2014 marked a significant milestone, being the first civilian satellite designed explicitly for InSAR analysis, and it produces free and open access data. In this study, we illustrate the potential of InSAR to detect the slow movement of landslide deposits in Gisborne before rapid acceleration, using Sentinel-1 data. The pre-failure deformation of several previous landslides in Gisborne is measured to determine possible deformation thresholds for rapid acceleration across the urban area.

In the relatively short and steep catchments of New Zealand’s Alps and Front Range, river systems traverse several process domains, from steep boulder-bed cascades to shallower braided range-front streams. Headwater streams (slope gradient >0.1 m·m-1) typically operate in a state of ‘supply limited’ conditions, where the river’s ability to carry sediment far exceeds the supply of material from upstream. With the catastrophic delivery of 13M m3 of landslide detritus following the 2016 7.8 Mw Kaikōura Earthquake, a tributary of the upper Hapuku River was filled to depths of up to 30 m, as debris spilled 1 km downstream from the delivery point. Nine airborne LiDAR surveys along the 12 km corridor have captured the transformation of the system from step-pool cascade to an unstable aggrading braidplain deposit to a vigorously incising channel, within four years of the event. With this rare window into disequilibrium conditions, we document the dramatic shifts in channel behaviour and dramatic reworking of the debris train following the landslide. There are two distinct phases: (1) a highly dynamic and unstable aggradation phase, with supply from upstream greatly exceeding river transport capacity and (2) exhaustion of supply from upstream and downcutting, maintaining high sediment transport rates through recruitment of material in the valley deposit. With a catchment area of only 3 km2, the upper river has transferred more than 4.2×106 m3 of coarse-grained material in 9 storm events of relatively modest intensity. This sequence of surveys provides an unprecedented picture of dramatic changes to a steepland river system in the aggradation/degradation cycle, which are very seldom captured owing to both the remoteness of such sites and the relative rarity of such events. A temporal picture of the valley sediment budget demonstrates the remarkable capacity of alpine systems to absorb disturbance through storage in the upper reaches, modulating the timing and the sedimentary character of materials being transferred to the reaches downstream. The case study highlights the utility of repeat LiDAR surveys for large-scale process studies and provides insights for assessing residence times of major landslide deliveries following large earthquake events.

The headwater catchment of the Siem Reap River has supplied the Angkor Temple Complex and surrounding communities since the twelfth century. The Angkor Temple Complex area consists of historical moats and barays (reservoirs) which are currently used to store the water from the Siem Reap River to maintain temple foundation, irrigate cultivation areas and provide floodwater storage. The Angkor Wat Temple, which is located in the complex, was constructed on a sandy alluvial substrate and needs a stable supply of water to avert land subsidence and destabilization of the temple foundation. In light of changing climate, land use and land cover (LULC) trends, it is crucial to examine the wide-ranging implications of reduced water supply for the Angkor Temple Complex. Using the Soil and Water Assessment Tool, this study seeks to assess the conditions necessary to provide sustainable streamflow to the Angkor Temple Complex. We modelled 30 scenarios of co-varied LULC and precipitation regime under a changing climate. The results show that under most LULC scenarios, sufficient water resources can be harvested to supply the complex—however—any further loss of forest cover is likely to impact groundwater conditions, flood management and dry season shortages. Conversely, the water supply to the complex is shown to be sensitive under the range of climate scenarios explored; a reduction of more than 10–20% in mean annual precipitation was enough to put the water supply under stress for the current and future conditions of the complex.

The Waiapu River catchment (drainage area of 1734-km2) is one of the most prolific conveyors of sediment in the world, annually delivering roughly 35 Mt of fine material to the ocean from eroding gullies, hillslopes, and reworked sediment on valley floors. Tectonic and geologic influences, in combination with a dynamic climate influenced by tropical cyclones and clearance of vegetation from steep hillslopes, predisposes this region to high rates of erosion. The bedload sediment regime of the river is strongly influenced by several exceptionally large gullies and gully complexes that produce a coarse-grained, poorly sorted sediment mixture. Rapid abrasion and breakdown leads to high rates of suspended sediment yield. A wave of bedload material, manifesting as elevated bed levels and significant widening of active alluvial fills, has been triggered by large inputs of hillslope material from a few key tributary catchments following Cyclone Bola in 1988. We review the evidence for the relaxation process of the sedimentary system in the subsequent 29 years, appraising some of the legacy effects that may endure, as associated with reworking of the considerable alluvial stores within the Waiapu system. We use Structure-from-Motion (SfM) techniques and archival aerial photos to quantify changes in sediment storage at the base of two major gully systems in recent decades. A record of over 850 cross section surveys at 62 sites on 10 rivers throughout the catchment (1958–2017) indicates recent transition from a trend of continuous accumulation to downcutting and remobilisation of valley-bottom deposits. The channel cross sections provide a minimum estimate of sediment flux from source areas to the lower reaches of the river, giving a rudimentary but spatially extensive picture of the wave of material cascading through the drainage network. The largest impacts occur in the upper steepland rivers, closest to the landslide-derived sediment supply. Transport rates here, as inferred from cross section change, are at a maximum during an aggradational phase following Cyclone Bola then taper off, despite the large sediment accumulations remaining in the system. As of 2017, the river is in the process of incising the upper extents of this deposit on a trajectory of recovery toward pre-Bola conditions. The compilation of cross section data provides us with new insights into the sensitivity of particular sites in the landscape, as well as the changing relationship between reach sediment storage and transport rates during the response and relaxation phase of a major disturbance in a large catchment.

Recent intensification of slope thermokarst is transforming permafrost preserved glaciated landscapes and causing significant downstream effects. In this paper we: A) Describe the thaw-related mechanisms driving the evolution of slope to stream connectivity; B) define the watershed patterns of thermokarst intensification; and C) project the cascade of effects through the Arctic drainage networks of northwestern Canada. The power-law relationships between disturbance area and volume, and thickness of permafrost thawed, in conjunction with a time-series of disturbance mapping show that the non-linear intensification of slope thermokarst is mobilizing vast stores of previously frozen glacial sediments linking slopes to downstream systems. Mapping across a range of catchment scales indicates that slope thermokarst predominantly affects first and second order streams. Slope sediment delivery now frequently exceeds fluvial transport capacity of these streams by several orders of magnitude indicating long-term perturbation. Mapping shows slope thermokarst is directly affecting over 6760 km of stream segments, over 890 km of coastline and over 1370 lakes across the 1,000,000 km2 Arctic drainage basin from continuous permafrost of northwestern Canada. The downstream projection of thermokarst disturbance increases affected lakes by a factor of 4 and stream length by a factor of 7, and suggests that fluvial transfer has the potential to yield numerous thermokarst impact zones across coastal areas of western Arctic Canada. The Prince of Wales Strait between Banks and Victoria Islands is identified as a hotspot of downstream thermokarst effects, and the Peel and Mackenzie rivers stand out as principle conveyors of slope thermokarst effects to North America’s largest Delta and to the Beaufort Sea. The distribution of slope thermokarst and the fluvial pattern of sediment mobilization signal the climate-driven rejuvenation of post-glacial landscape change and the triggering of a time-transient cascade of downstream effects. Geological legacy and the patterns of continental drainage dictate that terrestrial, freshwater and marine environments of western Arctic Canada will be a hotspot of climate-driven change through the coming centuries.

Typically, integrated coastal zone management (ICZM) uses the informed participation and cooperation of all stakeholders to assess the societal goals in a given coastal area. ICZM seeks, over the long term, to balance environmental, economic, social, cultural and recreational objectives, all within the limits set by natural dynamics. We outline coastal instability in the Auckland region of New Zealand, where the effects of natural coastal dynamics appear to have been underplayed, or even overlooked, during the residential land development process. Auckland is New Zealand’s largest city, with the Auckland region encompassing c. 3,300 km of coastline, with a highly variable wave climate and coastal geomorphology. The sparsely inhabited high energy west coast records significant wave heights of 2-3 m for much of the year. In contrast, the eastern bay coastlines are lee coasts, protected by offshore islands in the Hauraki Gulf and the Coromandel Peninsula. Nevertheless, significant coastal cliff instability does occur along these eastern coasts, which are heavily populated, with houses often constructed within 10 m of the cliff edge. Coastal instability in the Beachlands area in particular, is part-conditioned by engineering properties of the cliff materials, which include soft, Pleistocene sediments. In particular, shear surfaces develop along clay-rich tephra layers, which are of low-permeability, leading to increased porewater pressure, and cliff failure. Despite the clear failure mechanisms, coastal protection works and routing of domestic stormwater over the cliffs has led to further coastal instability.

Globally, rivers systems are under considerable and increasing threat from multiple anthropogenic stresses, including different types of direct (e.g. channel engineering) and indirect human impacts (e.g. land cover and land use changes) that alter water and sediment dynamics. (Dis)connectivity relationships determine the source, timing and rates of water and sediment flux in catchments and thus their geomorphic sensitivity to disturbance. However, most river and catchment management plans overlook the role of sediment (dis)connectivity. Here we use examples from different environmental settings with different sediment-related problems to show how understandings of sediment (dis)connectivity can inform catchment-based management plans. We focus on concerns for river conservation and recovery, using examples from Austria, New Zealand and Australia. Finally, we present questions for practitioners to consider to appropriately contextualise management applications when using (dis)connectivity concepts in practice. Our findings revealed that differences in sediment (dis)connectivity relationships exert profound catchment-specific variability in (eco)-geomorphic response to disturbance. Understanding (dis)connectivity and system history is therefore essential to forecast the effects of on-ground management actions.

Siem Reap River plays a crucial role in maintaining the stability of the Angkor Temple Complex and the livelihoods of the people in the basin. Land use and land cover (LULC) have changed considerably over the last few decades, as well as climatic regime, and these, in turn, have an influence on streamflow. The objective of this study was to assess the potential impacts of future LULC and climate change on streamflow upstream from the Angkor Temple Complex. LULC maps, classification of LULC units, and projections of change were developed using Maximum Likelihood Supervised Classification and the Land Change Modeler (LCM). Artificial neural network (ANN) downscaling was applied to downscale precipitation and temperatures. The Soil and Water Assessment Tool (SWAT) was applied to assess the effects of future LULC and climate change within the upper Siem Reap catchment. The Mann-Kendall test was employed to detect any potential trends within the current and future (modelled) streamflow. The results indicate that there would be reduction of streamflow at seasonal and annual timescales, under every scenario. The annual average streamflow was reduced −69%, −63% and −75% under the Representative Concentration Pathway (RCP) scenarios RCP 2.6, RCP 4.5 and RCP 8.5 respectively. It seems that there is a sufficient water supply to sustain the Angkor Temple Complex under the current LULC and climate regime, but there would be an insufficient water supply under every future modelled scenario. Moreover, trends in groundwater levels must be taken into account, because growing population will inevitably influence groundwater balance and surface water which could potentially threaten the stability of Angkor Wat Temple, a UNESCO World Heritage Site.

Cambodia is one of the most vulnerable countries to climate change impacts such as floods and droughts. Study of future climate change and drought conditions in the upper Siem Reap River catchment is vital because this river plays a crucial role in maintaining the Angkor Temple Complex and livelihood of the local population since 12th century. The resolution of climate data from Global Circulation Models (GCM) is too coarse to employ effectively at the watershed scale, and therefore downscaling of the dataset is required. Artificial neural network (ANN) and Statistical Downscaling Model (SDSM) models were applied in this study to downscale precipitation and temperatures from three Representative Concentration Pathways (RCP 2.6, RCP 4.5 and RCP 8.5 scenarios) from Global Climate Model data of the Canadian Earth System Model (CanESM2) on a daily and monthly basis. The Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) were adopted to develop criteria for dry and wet conditions in the catchment. Trend detection of climate parameters and drought indices were assessed using the Mann-Kendall test. It was observed that the ANN and SDSM models performed well in downscaling monthly precipitation and temperature, as well as daily temperature, but not daily precipitation. Every scenario indicated that there would be significant warming and decreasing precipitation which contribute to mild drought. The results of this study provide valuable information for decision makers since climate change may potentially impact future water supply of the Angkor Temple Complex (a World Heritage Site).

Ice-marginal glaciated landscapes demarcate former boundaries of the continental ice sheets. Throughout circumpolar regions, permafrost has preserved relict ground ice and glacigenic sediments, delaying the sequence of postglacial landscape change that transformed temperate environments millennia earlier. Here we show that within 7 × 10 6 km 2 of glaciated permafrost terrain, extensive landscapes remain poised for major climate-driven change. Across northwestern Canada, 60–100-km-wide concentric swaths of thaw slump–affected terrain delineate the maximum and recessional positions of the Laurentide Ice Sheet. These landscapes comprise ∼17% of continuous permafrost terrain in a 1.27 × 10 6 km 2 study area, indicating widespread preservation of late Pleistocene ground ice. These thaw slump, relict ground ice, and glacigenic terrain associations are also evident at the circumpolar scale. Recent intensification of thaw slumping across northwestern Canada has mobilized primary glacial sediments, triggering a cascade of fluvial, lacustrine, and coastal effects. These geologically significant processes, highlighted by the spatial distribution of thaw slumps and patterns of fluvial sediment mobilization, signal the climate-driven renewal of deglaciation and postglacial permafrost landscape evolution.

Large wood (LW) commonly forms log jams, influencing bed composition and biota via complex flow-sediment-wood interactions. A LW blockage, often induced by river-crossing infrastructure, can strongly alter channel hydraulics and sediment transport patterns, thus inducing a ‘forced’ channel morphology. For studying the deposition of bedload gravel fractions in the presence of a rigid LW jam, a novel experimental setup is presented. Using a mobile bed stream table, the effects of a channel-spanning blockage (a ‘dam jam’), resting at a bridge pier, on sediment transport and scour dynamics are examined. Changes in channel morphology were measured using Structure from Motion (SfM) photogrammetry and manually obtained bedload measurements. For the experiment without LW accumulation in place, natural bedload transport was observed over the entire channel length - about 20% of fed colour gravel was recovered from the sediment trap at the outlet, while a total bedload interruption occurred in presence of the LW accumulation, resulting in trapping all fed gravel material upstream of the obstructed cross-section. The volumetric deviation between SfM and manual measurements was less than 0,4%. The porosity characteristics of the LW accumulation were analysed using volumetric meshing techniques. With our experiments, we demonstrated that a relatively high log jam porosity has significant impact on channel morphology. By interrupting the hydraulic energy gradient, the movement of coarse sediment transport is damped, forcing deposition and initiating the development of a sediment wedge upstream of the infrastructure. Our quantitative results provide new insights into how LW can force channel morphology (particularly sediment storage) through the alteration of channel hydraulics. We further elaborate on how novel laboratory-based SfM techniques can be used to enhance the current understanding of complex flow-sediment-wood interaction processes at engineered in-stream structures.

The formation of large wood (LW) accumulations during floods represents a major hazard for constricted river cross-sections, e.g. bridges and weirs, as it affects flow hydraulics and sediment transport. To better assess LW accumulations, reliable strategies and techniques are required. There are currently practical limits on monitoring accumulation configurations. Both laser scans and photogrammetric techniques can be used to scan the outer contours of LW accumulations, but cannot practically assess the wood content and porosity. Details of the outer deposit are captured in high resolution, but the core of the deposit remains occluded, and estimation is necessary. This becomes more challenging for deposits of increasing size (relative to wood elements). To develop a more efficient workflow for LW accumulation assessment in the field, we performed a laboratory study to develop a relationship between the envelope volume of water-worked LW jams during a single flood hydrograph and the volume of woody elements within (explicitly accounting for porosity). We used photogrammetric techniques, now in common use for reconnaissance surveys of debris accumulations, on wood accumulations scaled for the laboratory. The study's aim is to develop a semi-automated assessment method, enabling efficient image acquisition, processing and computation of LW accumulation volume. Using a multi-camera array above the laboratory channel, and applying Structure from Motion photogrammetry, we developed 3D models for 16 experimental flow-formed wood accumulations, each with >50 individual wooden dowels. No correlations were found between porosity and flow magnitude; porosity was found to be similar for most deposits (~66%). As a result of this accumulation structure, the envelope volume used in 3D and 2.5D photogrammetric methods tended to overestimate wood content by 3× and 2.6×, respectively. The results obtained here will contribute to a more reliable volumetric assessment for inventories of wood mass in river systems.

Chilliwack River is typical of many Cordilleran valley river systems that have undergone dramatic Holocene degradation of valley fills that built up over the course of Pleistocene glaciation. Downstream controls on base-level, mainly blockage of valleys by glaciers, led to aggradation of significant glaciofluvial and glaciolacustrine valley fills and fan deposits, subsequently incised by fluvial action. Models of such large-scale, long-term degradation present a number of important challenges since the evolution of model parameters, such as the rate of bedload transport and grain size characteristics, are governed by the nature of the deposit. Sediment sampling in the Chilliwack Valley reveals a complex sequence of very coarse to fine textural modes. We present a 1-D numerical morphodynamic model for the river-floodplain system tailored to conditions in the valley. The model is adapted to dynamically adjust channel width to optimize sediment transporting capacity, and to integrate relict valley fill material as the channel incises through valley deposits. Sensitivity to model parameters is studied using four principal criteria: profile concavity, rate of downstream grain-size fining, bed surface sand content, and the timescale to equilibrium. Model results indicate that rates of abrasion and coarsening of the grain size distributions exert the strongest controls on all of the interrelated model performance criteria. While there are a number of difficulties in satisfying all model criteria simultaneously, results indicate that 1-D models of valley-bottom sedimentary systems can provide a suitable framework for integrating results from sediment budget studies and chronologies of sediment evacuation established from dating.

A Structure from Motion (SfM) photogrammetry-based methodology for precise mapping of large wood (LW) accumulations in fluvial systems is presented. The technique may be useful for routine inventory and rapid volume estimation of complex LW structures that tend to divert or obstruct flow in rivers. Our methodology is validated by means of laboratory experiments, ranging from elementary to complex arrangements of LW components and organic fine material (OFM). Seven experimental setups were used as the basis for (i) manual approximations of 2.5D and 3D geometric reference volumes, (ii) 2.5D volume models based on mesh geometry, (iii) a closed (‘watertight’) 3D mesh from an unorganized point cloud and (iv) estimates of porosity. A commercially available SfM photogrammetry software package, Pix4Dmapper, was used for point cloud and simplified mesh generation. In order to obtain more precise volumes, 3D surface models are required. Accordingly, we generated 3D watertight mesh models of the unorganized point cloud using the screened Poisson Surface Reconstruction (PSR) technique. The Pix4D volume tool (2.5D) resulted in an overestimation (2.9 to 52.7%) of the geometric volume (3D), due to the convex hull approximation of the geometry normal to the surface plane. PSR (3D) resulted in more precise volumes, showing deviations from the geometric volume (3D) in a range of −15.9 to +10.6%, as the algorithm could capture concavities and involuted surfaces on the accumulation. Assuming that the difference between 3D and 2.5D volume models represents many of the voids visible within or on the surface of the deposit, this volume can be used as an estimate of porosity. Our assessment suggests that image-based SfM methodology is well-suited for further investigations in LW research, due to its time and cost efficiency in comparison with other conventional surveying techniques. The methodology can be used to generate high quality point cloud and mesh models of log jam formations; these may be used by river managers and researchers to quantify accumulation volume and thus gain a better understanding of LW composition and the influence of wood geometry on hydraulic flow conditions.

River systems in forested catchments are strongly influenced by wood and sediment loading from both natural (e.g. mass wasting) and anthropogenic (forestry) sources. In order to effectively manage impacts on property, infrastructure and the broader ecosystem, as well as to better assess the interactions between large wood (LW), channel morphology and flow hydraulics, more efficient and accurate surveying techniques are required. We present an evaluation of Structure from Motion (SfM) photogrammetry and point-cloud-based techniques for capturing the geometry and volume of LW in the field. Wood accumulations can be notoriously complex 3D objects, with multi-scalar features, and thus difficult to quantify with photogrammetric methods. We introduce a novel workflow to generate volumetric information of organic material accumulations, using SfM and a suite of meshing algorithms. The volumes of two accumulations are assessed individually, using several meshing techniques, and are compared with more conventional volume estimates. Results show volumetric variations of

Large wood (LW), delivered to the river channel in the course of commercial forest harvesting, or generated during natural events, can be mobilised during floods. The movement of wood along the river corridor involves complex cycles of recruitment, mobilisation, transportation and deposition. These processes are affected by the size, buoyancy, roughness and complexity of the wood components, as well as the relative spatial density and the character of the channel boundary elements. In order to understand the probabilistic behaviour of woody elements within the fluvial system, it is important to be able to characterise the timing, mechanisms and duration of the various phases of wood transport. Due to a lack of suitable sensing technology, a detailed understanding of LW recruitment, transport and accumulation processes has thus far been elusive. In this study we introduce a technique using a nine-degrees of freedom (9-DoF) sensor embedded in a ‘SmartWood’ dowel that shows strong potential for measuring and recording LW movement. The SmartWood assembly comprises an integrated sensor with an inertial measurement unit (IMU), accelerometer, gyroscope and magnetometer, installed in a wooden dowel that is scaled to represent a tree stem in the flume. The sensor is able to record the many different motions of LW transport. The sensor-tagged wood dowel is density-compensated, with a specific weight of 0.5 g·cm−3. A series of verification and experimental tests was carried out to evaluate the applicability of this new technology for LW research and is presented herewith. Experiments were conducted in a 6.3 m long and 1.5 m wide flume with sinuous channel course and mobile gravel bed conditions, with a discharge of up to 10 l·s−1. We show that LW movement during transport, particularly starting, rolling, yawing and stopping processes, but also LW impacts, can be quantified within a flume environment. These findings can be further developed to obtain the translational movement behaviour of LW, which is needed to refine probabilistic models of downstream trajectories. Understanding complex LW movement is essential for informing freshwater and forestry management guidelines.

[1] Ice-cored permafrost landscapes are highly sensitive to disturbance and have the potential to undergo dramatic geomorphic transformations in response to climate change. The acceleration of thermokarst activity in the lower Mackenzie and Peel River watersheds of northwestern Canada has led to the development of large permafrost thaw slumps and caused major impacts to fluvial systems. Individual “mega slumps” have thawed up to 106 m3of ice-rich permafrost. The widespread development of these large thaw slumps (up to 40 ha area with headwalls of up to 25 m height) and associated debris flows drive distinct patterns of stream sediment and solute flux that are evident across a range of watershed scales. Suspended sediment and solute concentrations in impacted streams were several orders of magnitude greater than in unaffected streams. In summer, slump impacted streams displayed diurnal fluctuations in water levels and solute and sediment flux driven entirely by ground-ice thaw. Turbidity in these streams varied diurnally by up to an order of magnitude and followed the patterns of net radiation and ground-ice ablation in mega slumps. These diurnal patterns were discernible at the 103 km2 catchment scale, and regional disturbance inventories indicate that hundreds of watersheds are already influenced by slumping. The broad scale impacts of accelerated slumping are indicated by a significant increase in solute concentrations in the Peel River (70,000 km2). These observations illustrate the nature and magnitude of hydrogeomorphic changes that can be expected as glaciogenic landscapes underlain by massive ice adjust to a rapidly changing climate.

The Peel Plateau is a fluvially incised, ice-rich moraine landscape that extends along the eastern margins of the Richardson and Mackenzie Mountains, northwestern Canada. The 24,000 km2 region demarcates the western boundary of the former Laurentide Ice Sheet (LIS). Landscape form and geomorphic processes are strongly conditioned by terrain assemblages produced during the advance and retreat of the LIS and by the large stores of relict late Pleistocene ground ice preserved in permafrost. Holocene fluvial, slope, and thermokarst activity has reshaped this landscape. Fluvial incision of the plateau and an abundance of ground ice favor the development of retrogressive thaw slumps. Recent warming and increasing rainfall have given rise to large, long-lived instances of these thermokarst features. We discuss the morphology, processes, and climate feedbacks that control their development. Thaw slump activity on the Peel Plateau provides insight on the geomorphic processes that are likely to dominate the evolution of ice-rich glacigenic landscapes under rapidly changing climate conditions.

The term sediment flux refers to sediment movement through landscapes. Analogous to “flux” in physics, i.e., the rate of flow of a property per unit area, sediment flux is the amount of sediment that flows through a cross-section of river per unit time. The magnitude of sediment flux is moderated by catchment processes such as sediment production (erosion), sediment accumulation (deposition) and intervening processes of sediment storage and reworking (transfer). Patterns and rates of sediment flux vary over a wide range of spatial and temporal scales, from grain to grain and landform scale analyses over near instantaneous timeframes through reach and catchment-scale analyses that are typically performed over decadal to millennial timescales to continental-scale appraisals over millions of years. Sediment movement is a key physical driver of natural environments. It exerts a critical influence upon the morphology, process regime, and evolutionary traits of landscapes. For example, as sediment budgets quantify sediment transport pathways, they can be used to analyze the critical factors that affect landscape development. Sediment flux exerts a critical influence upon the physical template (habitat distribution) of river systems. As such, it is a key consideration in river management and restoration. Analysis of source-to-sink relationships at the catchment scale (and associated sediment budgets) highlights controls upon sediment delivery and the influence of landscape connectivity. Emphasis here is placed upon valley floor processes, giving only partial attention to hillslope forms and processes or consideration of lakes, deltas, and nearshore marine environments. Textbooks and journals that present overviews of sediment flux in river systems are considered first. A brief overview of global scale sediment flux summarizes the movement of sediment from terrestrial areas to the ocean and the imprint of human activities. Most of this contribution focuses on catchment-scale sediment budgets, emphasizing variability in sediment sources (hillslope inputs and reworking on valley floors), the thorny question of scale relations, controls upon the sediment delivery ratio, and the influence of landscape connectivity. In many instances, disturbance events disrupt the sediment regime of a river, creating distinct pulses (or waves) that are transferred downstream by dispersion or migration processes. This is followed by an analysis of approaches to measurement of sediment flux, differentiated in relation to conventional field techniques, use of sediment fingerprinting, and the emergence of a range of remotely sensed technologies. The final sections of this article outline implications of human-induced alterations to sediment flux for river management. Appraisal of sediment disasters (impacts of dams, fine-grained sediment accumulation, and mining activities) is followed by an assessment of implications for river restoration.

The paraglacial reworking of glacial sediments by rivers and mass wasting is an important conditioning factor for modern sediment yields in mountainous catchments in formerly glaciated regions. Catchment scale and patterns of sediment storage are important influences in the rate of postglacial adjustment. We develop a quantitative framework to estimate the volume, sediment type, and fractional size distribution of legacy glacial materials in a large (1230 km2) watershed in the North Cascade Mountains in south-western British Columbia, Canada. Chilliwack Valley is exceptional because of the well-dated bounds of deglaciation. Interpolation of paleo-surfaces from partially eroded deposits in the valley allows us to estimate the total evacuated sediment volume. We present a chronology of sediment evacuation from the valley and deposition in the outlet fan, based on infrared stimulated luminescence (IRSL) and 14 C dating of river terraces and fan strata, respectively. The effects of paraglacial sedimentation in Chilliwack Valley were intensified through a major fall in valley base-level following ice retreat. The steepened mainstem valley gradient led to deep incision of valley fills and fan deposits in the lower valley network. The results of this integrated study provide a postglacial chronology and detailed sediment budget, accounting for long-term sorting of the original sediments, lag deposit formation in the mainstem, deposition in the outlet fan, and approximate downstream losses of suspended sediment and wash load. The mass balance indicates that a bulk volume of approximately 3.2 km3 of glacial material has been evacuated from the valley. Copyright © 2012 John Wiley & Sons, Ltd.

Tunnicliffe, J., Church, M. & Enkin, R. J. 2012 (January): Postglacial sediment yield to Chilliwack Lake, British Columbia, Canada. Boreas, Vol. 41, pp. 84–101. 10.1111/j.1502-3885.2011.00219.x. ISSN 0300-9483. Seismic records and evidence from sediment cores at Chilliwack Lake provide the basis for a long-term (postglacial) sediment budget for a 324-km2 Cordilleran catchment. Chilliwack Lake (11.8 km2 surface area), situated in the North Cascade Mountains, near Chilliwack, British Columbia, was formed behind a valley-wide recessional moraine in the final phase of post-Fraser alpine glaciation. Seismic surveys highlight the postglacial lacustrine record, which is underlain by a thick layer of sediments related to deglacial sedimentation. Sediment cores provide details of grain-size fining from the delta to the distal lake basin. The cores also show a record of intermittent fire and debris flows. Magnetic measurements of lake sediments provide information on grain size, as well as a dating framework. The total postglacial lake-floor deposit volume is estimated to be 397 ± 27 × 106 m3. Including estimates of fan and delta deposition, the specific postglacial yield to the lake is calculated to be ∼86 ± 13 Mg km2 a−1. The sediment volume in the uppermost (Holocene) lacustrine layer is 128 ± 9 × 106 m3, representing ∼41 ± 4 Mg km2 a−1 in the Holocene. Compared with other Cordilleran lakes of similar size, particularly those with glacial cover in the watershed, Chilliwack Lake has experienced relatively modest rates of sediment accumulation. This study provides an important contribution to a growing database of long-term (postglacial) sediment yield data for major Cordilleran lakes, essential for advancing our understanding of the pace of landscape evolution in formerly glaciated mountainous regions.

The Holocene volumetric sediment budget is estimated for coarse textured sediments (sand and gravel) in a large, formerly glaciated valley in southwest British Columbia. Erosion is estimated by compiling volumetric loss estimated in digital elevation models (DEMs) of gullied topography and by applying a non-linear diffusion model on planar, undissected hillslopes. Estimates of steepland yield are based on estimates of post-glacial deposition volumes in fans, cones and deltas at the outlets of low-order tributary catchments. Erosion of post-glacial fans and tributary valley fills is estimated by reconstructing formerly continuous surfaces. Results are classed by catchment order and compared across scales of contributing area, revealing declining specific sediment yield (in m3 km−2 a−1) with catchment area for the smaller tributaries (

Magnetically tagged particles were used to investigate the effects of sockeye salmon (Oncorhynchus nerka) and floods on the dispersion of coarse bed material in the Stuart-Takla region, British Columbia, Canada. The dominant annual sediment transporting event in the channels is the snowmelt flood events, with lesser activity usually accomplished during summer floods. Annually in August, the channel bed material is reworked by the Early Stuart sockeye salmon spawning, as the fish excavate the streambed to deposit and bury their eggs. These nesting cavities are called redds. Results from 67 tracer recovery experiments over five years were highly variable, subject to the magnitude of floods and the returning population of salmon. Overall, the depositional pattern from nival flood events usually demonstrated a high degree of clast mobilization, long travel distances (up to 150 m), and mean depths of burial up to 18 cm. Summer flood events showed somewhat lower rates of mobilization, distances of travel, and depths of burial. Although the fish did not move the tracers very far, their effect on the bed was generally quite pervasive - up to 100 percent of the clasts were mobilized, and the depth of burial was considerable (mean burial depths up to 14 cm). The amount of vertical mixing of sediment by salmon was often on the same order of magnitude as flood events. The significant vertical mixing of sediments by the fish has important implications for the mobility of sediment in the stream. Since any armoring layer formed during high flows throughout the year is subject to the bioturbation of salmon, this suggests that the transport threshold in the creeks remains relatively low. Salmon likely play an integral role in the sediment transport dynamics and annual sediment budget of the lower reaches of these creeks.

A bedload movement detector of novel design was installed in a gravel-bed stream as a component of the ongoing research on sediment transport dynamics in the Stuart–Takla Experimental Watersheds in north-central British Columbia, Canada. The device is designed to collect information on the patterns and timing of bedload transport during a flood event. The device is based on a passive magnetic sensor that produces signals of 10−2 to 10−5 V as its magnetic field is disturbed by passing clasts. A series of 82 sensors is housed in an aluminum beam placed across the stream, inserted such that its surface is flush with the gravel bed. The device can be raised or lowered to compensate for bed aggradation and scour. A data acquisition system gathers voltage signals from the sensors at rates of 30 to 100 Hz. This device is sensitive enough to record the movement of most volcanic, metamorphic, granitic and ultramafic clasts larger than a few millimetres. O'Ne-ell Creek watershed is a 68 km2 tributary basin of the Middle River drainage system in the northern headwaters of the Fraser River. Bedload transport generally occurs twice a year in the Stuart–Takla streams: once during spring floods and again during salmon spawning activity. Bedload moved only during two days in 1998, at the peak of the relatively small nival flood in May. Nevertheless, the device detected at least 3×106 passing clasts. A continuous record of bedload transport was obtained, showing: a pulsating pattern of activity seemingly independent of stage, lateral movement of the transport zone, and a sudden onset of bed movement with a tapered cessation. We anticipate that more sophisticated calibration of the sensors and accelerated sampling rates will provide detailed information on the size and/or velocity and magnetic permeability of particles moving over the device, and will contribute to a better understanding of bedload transport. Copyright © 2000 John Wiley & Sons, Ltd.

[1] Analyses of bed load transport data from four streams in British Columbia show that the activity of mass spawning salmon moved an average of almost half of the annual bed load yield. Spawning-generated changes in bed surface topography persisted from August through May due to lack of floods during the winter season, defining the bed surface morphology for most of the year. Hence, salmon-driven bed load transport can substantially influence total sediment transport rates, and alter typical alluvial reach morphology. The finding that mass-spawning fish can dominate sediment transport in mountain drainage basins has fundamental implications for understanding controls on channel morphology and aquatic ecosystem dynamics, as well as stream responses to environmental change and designing river restoration programs for channels that have, or historically had large spawning runs.